Motor vehicle manufacturers use on-board gas sensors to monitor exhaust gases, for engine control purposes and/or for determining the performance of a catalytic converter treating engine exhaust gases as they are passed by the exhaust conduit from the engine to the atmosphere. Sensors of this type must be sufficiently robust to withstand the high temperatures and aggressive gases to which the sensor is exposed in the exhaust conduit, including elevated temperatures typically of about 500.degree.-600.degree. C., temperature cycling, vibration, intermittent moisture, etc. Sensors of this type used to date are disadvantaged by the need for electrical leads and shielding near the active part of the sensor. Typically, such known sensors produce an electrical signal which varies in relation to the oxygen content level of the exhaust gas. The sensor output signal may be used as an input to an electronic engine control means, such as for an electronic engine control module controlling the air/fuel mixture which is fed at any given point in time to a combustion chamber of the engine. Maintaining the integrity of the electrical connections to the sensor presents a challenge in the field of motor vehicle engine control. In addition, a problem is presented in maintaining the correct functioning of the active sensor material exposed to the harsh environment of the exhaust conduit.
It is an object of the present invention to provide an on-board gas composition sensor suitable for monitoring oxygen content in the exhaust gas of an internal combustion engine. In particular, it is an object of the invention to provide a robust gas composition sensor having good response time, good durability in the exhaust gas environment, and avoiding some of the disadvantages of the known exhaust gas oxygen sensors. These and additional objects of the invention will be understood from the following disclosure and detailed description of certain preferred embodiments.